Confounding their mystery is that Titan's dunes aren't even made of sand. When ultraviolet light from the sun breaks apart methane high in Titan's atmosphere, it produces ethane and hydrogen. When these chemicals coalesce into particles, they settle out as a tar-like rain. Therefore, dune material literally falls out of Titan's skies as solid hydrocarbon grains the size of coarse sand.
Don't imagine Dune's giant sand worms or Star Wars' elephant-like Banthas among the dunes. Cryo-life on Titan would be strictly microbial, and undergo metabolism at a snail's pace.
The hydrocarbon sand is blown northward from the dry southern hemisphere where it builds up dunes along an equatorial belt. Saturn's slightly elliptical orbit means that Titan's southern hemisphere has short intense summers. This makes the southern regions drier. The arid sand is transported by the winds to make dunes.
Given this washboard terrain, engineers imagine future robotic explorers to Titan being balloons that survey the great dune fields, volcanoes and methane seas and lakes.
My favorite drawing board design is called the TALE (Titan Airship Latitude Excursion). The nuclear-powered buoyant gas airship would have enough propulsion to travel at different latitudes, hence survey the Titan landscape from polar lakes to equatorial dunes. It would have a steerable antenna for data relay, the ability to pull up surface samples via a tether, and have an onboard organic analysis laboratory.